Technical Abstract:
Although it is well known that Ca is more effective in flocculating clays than Mg at an equal electrolyte concentration the molecular mechanisms underlying this behavior are not well understood. We studied both macroscopic and molecular properties of Ca- and Mg-saturated soil clays in relation to their flocculation behavior. We measured d-spacing of the clays susing x-ray diffraction to determine if Mg-saturation results in greater separation distance of clay layers than Ca-saturation. Amount and status of absorbed water on soil clays was measured using a combination FTIR-gravimetric approach. Electrophoretic mobility was determined to estimate the size of the electric double layer of soil clays. It was found that Mg-clays absorbed more water than Ca-clays. They also exhibited enhanced hydrogen boding. These differences between Ca and Mg clays were not reflected in observed d-spacing. This suggested that the additional water sorbed to the Mg-clay is located between the cations in the interlayers. In this case, it should not affect flocculation. Alternatively, water can be localized between clay platelets, where it cannot be determined using x-ray diffraction.